The present invention relates to an arrangement for a piston-and-cylinder unit.
Piston-and-cylinder units are frequently located in an outdoor environment, exposed to varying temperatures, air humidity, and the like, each of which provide a breeding ground for corrosive attacks. Examples of such piston-and-cylinder units might be so-called xe2x80x9cgas springsxe2x80x9d or xe2x80x9cgas dampersxe2x80x9d for force balancing and damping of various kinds of doors or lids. EP-A1 -0 364 851 discloses a piston-and-cylinder unit which is an example of a method for reducing the corrosion problems. This piston-and-cylinder unit exhibits a closure portion consisting of a bush enclosed by an end portion of a barrel pipe of the piston-and-cylinder unit. The end portion is bent inwards, towards the piston rod extending through the bush, so as to terminate the cylinder barrel with a circumferential edge that is generally directed perpendicularly to the longitudinal direction of the barrel pipe; that is, the axial direction of the piston-and-cylinder unit. The barrel pipe is usually made of a resistant and relatively easily workable material, such as carbon steel, which is corrodible. Because of this, the barrel pipe is surface treated with corrosion-protective coatings, normally a pretreatment and one or more coats of lacquer. It has, however, turned out that the circumferential edge receives a thinner coat of lacquer which results in corrosion attacks over time. This limits the service life of the cylinder unit in many applications. On the piston-and-cylinder unit according to the referenced publication, a separate component has therefore been arranged in the form of a resilient protection ring of rubber, plastic or similar material, that covers the end portion of the barrel pipe and its inward-directed circumferential edge. Through this, a certain weather protection is obtained, as long as the protection ring is undamaged. These rings of plastic, rubber, and the like, however, have a limited service life and may also cause condensation that is not ventilated off and therefore can create corrosion problems. Furthermore, such a protection ring entails an additional component that adversely affects the cost of this piston-and-cylinder unit.
In view of the above described deficiencies associated with conventionally designed piston-and-cylinder devices, the present invention has been developed. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to conventionally designed piston-and-cylinder devices and incorporates several additional beneficial features.
An object of the present invention is to provide an arrangement by which the corrosion problem described hereinabove is resolved without the need of dedicated sealing members. In a more specific example, a piston-and-cylinder arrangement is disclosed having a cylinder member and a piston member connected to a piston rod. The piston member and the piston rod are movable within the cylinder member. The cylinder member has a barrel pipe and closure portions at each of two ends thereof. One of the closure portions has a bush provided with a through bore in which the piston rod is located and enclosed. That end portion is bent radially inwards towards the piston rod and over a first circumferential surface of the bush. The bush has a collar portion that establishes an external second circumferential surface of the bush. The collar portion encloses the piston rod and extends axially beyond the inwardly bent portion. The inwardly bent portion of the barrel pipe terminates in a circumferential edge located adjacent to an inner corner of the bush formed between the first circumferential surface and the second circumferential surface.
In the presently disclosed arrangement, the barrel pipe may be provided with a highly covering corrosion protection, contributing positively to the service life of the piston-and-cylinder and-cylinder unit. Through utilizing the surface tension effects created at an inner corner according to the invention, improved lacquer coverage and a thicker coating layer is achieved, providing improved corrosion protection.
The beneficial effects described above apply generally to the exemplary devices, mechanisms and methods disclosed herein for piston-cylinder devices. The specific structures and methods through which these benefits are delivered will be described in detail hereinbelow.